Fuel supply unit

ABSTRACT

In a fuel feed unit ( 2 ) a bleed valve ( 9 ) is connected to a region which is constantly filled with fuel. This means that gases pass out of the fuel feed unit ( 2 ) through the bleed valve ( 9 ). However, penetration of gases when the fuel feed unit ( 2 ) is not operating, via leaks in the bleed valve ( 9 ), is reliably avoided.

DESCRIPTION

[0001] Fuel Feed Unit

[0002] The invention relates to a fuel feed unit, having a fuel pump, which is provided for the purpose of feeding fuel out of a suction region into a delivery region, and having a bleed valve for sealing the delivery region or connecting the delivery region to the environment.

[0003] Fuel feed units of this type are in widespread use in modern motor vehicles and are known in practice. The fuel feed unit generally has a fuel pump, which is arranged in a housing and has an electric motor, and is mounted in a splash pot in a fuel tank of the motor vehicle. In the installed state of the fuel feed unit, the fuel pump and the suction region are situated at a lower end of the housing. The delivery region with the bleed valve and a connection piece for a flow line leading to an internal combustion engine of the motor vehicle are arranged in the upper region of the housing. The fuel which is being fed generally flows through the electric motor.

[0004] A drawback of the known fuel feed unit is that when the splash pot is virtually empty after the fuel pump has been inactive for a prolonged period, air can penetrate into the housing via the bleed valve. Then, when the fuel pump is started up, this air must first of all be displaced back out by the fuel being fed, via the bleed valve. This leads to a time delay when building up pressure and to air and fuel mixing.

[0005] The invention is based on the problem of preventing air from penetrating into the housing of the fuel feed unit.

[0006] According to the invention, this problem is avoided by the fact that that end of the bleed valve which faces the environment is connected to a region which is constantly filled with fuel in the installed state of the fuel feed unit.

[0007] This arrangement means that it is impossible for any air to penetrate into the housing of the fuel feed unit according to the invention via the bleed valve. Therefore, the housing is full of fuel even after the fuel pump has been inactive for a prolonged period and does not have to be bled when the fuel pump is started up. The air which is present during the initial filling in the housing and gas bubbles which are produced as a result of gases evolved from the fuel can be discharged from the housing via the bleed valve without problems.

[0008] The fuel feed unit according to the invention is of particularly simple design if a line is connected to the environment-side region of the bleed valve, and if the line runs to close to the suction region. Consequently the free end of the line is always situated within the fuel, even when the splash pot is virtually empty.

[0009] The line may, by way of example, have a particularly large cross section and may store air which is to be discharged during the initial filling operation. However, the penetration of air situated in the line into the housing of the fuel feed unit according to the invention can be substantially avoided if the volume of the line is particularly small compared to the volume of the delivery region.

[0010] According to another advantageous refinement of the invention, a contribution is made to further reducing the storage volume of the line if the line has an angled portion leading to the suction region close to the bleed valve. This design makes the length of the line particularly short.

[0011] It is easy to prevent any obstacle to air escaping from the housing of the fuel feed unit according to the invention via the bleed valve if the free end of the line, when the fuel feed unit is mounted in a splash pot, is at a predetermined distance from the bottom of the splash pot.

[0012] The invention permits numerous embodiments. To further clarify its basic principle, one of these embodiments is illustrated in the drawing and is described below.

[0013] The only figure in the drawing shows a base region of a fuel tank of a motor vehicle. A splash pot 1 with a fuel feed unit 2, which has a two-stage fuel pump 3, is fitted in the fuel tank. The fuel pump 3 has a preliminary stage 4 for feeding fuel out of the fuel tank into the splash pot 1, and a principle stage 5 for feeding fuel out of the splash pot 1 into a delivery region 7 arranged in the upper part of a housing 6 of the fuel feed unit 2. For clarification, the flows of fuel are indicated by arrows in the drawing. A connection piece 8 for a flow line, which is not shown and leads to an internal combustion engine of the motor vehicle, is arranged on that part of the housing 6 which has the delivery region 7. Furthermore, the housing 6 has a bleed valve 9. The bleed valve 9 connects the delivery region 7 to the environment and allows gas bubbles to escape from the delivery region 7. When the delivery region 7 has been completely filled with fuel, the bleed valve 9 closes. A line 10, which leads to just above the bottom of the splash pot 1 and therefore into a region which is constantly filled with fuel, is connected at the environment-side end of the bleed valve 9.

[0014] When the delivery region 7 is vented, gases pass out of the delivery region 7 through the bleed valve 9 and the line 10. When the motor vehicle and therefore the fuel feed unit 2 are stationary, the fact that the line 10 runs as far as into the region which contains fuel prevents air from being able to enter the delivery region 7 as a result of leaks at the bleed valve 9. Consequently, pressure is built up particularly quickly when the fuel feed unit 2 is started up again. 

1. Fuel feed unit, having a fuel pump, which is provided for the purpose of feeding fuel out of a suction region into a delivery region, and having a bleed valve for sealing the delivery region or connecting the delivery region to the environment, characterized in that that end of the bleed valve (9) which faces the environment is connected to a region which is constantly filled with fuel in the assembled state of the fuel feed unit (2).
 2. Fuel feed unit according to claim 1, characterized in that a line (10) is connected to that end of the bleed valve (9) which faces toward the environment, and in that the line (10) leads to close to the suction region.
 3. Fuel feed unit according to claim 1 or 2, characterized in that the volume of the line (10) is particularly small compared to the volume of the delivery region (7).
 4. Fuel feed unit according to at least one of the preceding claims, characterized in that the line (10) is bent in a U shape.
 5. Fuel feed unit according to at least one of the preceding claims, characterized in that the free end of the line (10), when the fuel feed unit (2) has been mounted in a splash pot (1), is at a predetermined distance from the bottom of the splash pot (1). 